(1) Field of the Invention
The present invention relates to an ion implantation apparatus used in the manufacture of semiconductor elements, and more specifically relates to a batch ion implantation apparatus.
(2) Description of the Prior Art
Local impurity dopant implantation (ion implantation) to semiconductor wafers is performed by injecting an ion beam in part of a semiconductor wafer disposed in a vacuum chamber.
Generally this sort of local ion beam irradiation is performed by a method wherein a photoresist mask is patterned on a semiconductor wafer and the wafer is partially covered by the mask.
However, when an ion beam is irradiated to the photoresist mask, outgas such as moisture and organic matter is generated from the photoresist. This outgas accompanies the ion beam and is injected into the wafer, and generates crystal defects by affixing to the wafer surface. It accumulates on the wafer, interferes with the ion beam and decreases the implantation accuracy of the impurity dopant. Thus, outgas causes the production yield of the semiconductor wafer to decrease.
However, in this type of ion implantation apparatus, outgas generated from the photoresist mask is unavoidable, and the generation of outgas cannot be eliminated. Therefore, in order to improve the production yield in semiconductor wafer production, it is important to quickly remove outgas from the wafer surface.
As technology that removes outgas from the wafer surface, there is for example JP H11-204075A. JP H11-204075A discloses a wafer loading member of an ion implantation apparatus that includes a rotatably driven support portion, a wafer holding portion wherein a wafer disposed on a circumference made the center of this support portion is held, and an intermediate portion that supports the wafer holding portion around the support portion by linking this wafer holding portion and the support portion, wherein the intermediate portion includes a gas aspirating means that aspirates gas from the face of the side of the wafer holding portion where the wafer is held towards the back side of the wafer holding portion. JP H11-204075A is distinguished in that by this aspirating means outgas is aspirated and evacuated to the back side of the face where the wafer is supported.
With this technology, outgas is aspirated and evacuated to the back side of the face where the wafer is supported by a gas aspirating means, but with simple gas aspiration it is not possible to quickly remove generated outgas from the wafer. Thus, even using the technology disclosed in JP H11-204075A, the occurrence of crystal defects caused by newly generated molecules of outgas joining to the wafer surface cannot be adequately prevented.